Tarpaulins, or xe2x80x9ctarpsxe2x80x9d as they are commonly called, are used mainly as covers to protect material from moisture. However, as tarps have evolved from canvas to treated canvas to the reinforced polyvinyl tarps found today, their uses have increased dramatically. The versatility of any given tarp is usually limited only by its size, shape, and the number and location of attachment points so that the tarp can be secured.
One common application for large tarpaulin covers is the protection of large stockpiles of materials susceptible to water damage or being blown by wind. Examples include grains, salt, sand, and the like. It is not uncommon for large scale operations to store these commodities in stockpiles spanning several acres reaching heights of fifty feet to one hundred feet. Efforts to develop a tarpaulin cover system to protect a pile of this magnitude have been plagued with problems.
One such cover system, described in U.S. Pat. No. 3,949,527, used a network of tires and cables to secure large covers to the surface of a pile. The tires served to separate the cables from the cover. The network worked well to secure the cover and the tires protected the tarp from the cables, thereby leaving the watertight integrity of the cover intact. However, the tires would collect water. Given the mammoth proportions of these covers, the standing water collected by the tires produced concerns about health hazards such as encephalitis and other mosquito-related problems.
Another system, described in U.S. Pat. No. 4,879,970, used one or more covers, having webbing sewn into the cover material, and ground anchors to hold the cover down. A system using this method of anchoring was referred to as a xe2x80x9cbandedxe2x80x9d system. Alternatively, bags of ballast material could be hung from the webbing to secure the cover. A system using this method of anchoring was referred to as a xe2x80x9cballastxe2x80x9d system. Providing the two securing methods was a great advantage over the prior system. However, the webbing presented problems with keeping the covered material dry. Water would work its way through the webbing stitching, especially when the ballast bags were hung from the webbing, or when standing water formed on the top of a pile.
Maintaining a watertight cover over most materials is of paramount importance. Salt is an example of such a material. Salt is stored in huge piles. If standing water develops on top of such a pile, and a leak develops, the salt under the cover dissolves as it gets wet. This causes a dent in the top of the pile to form, thereby creating a place for more water to collect, perpetuating the leak, and increasing the size of the dent. It is not uncommon to lose on the order of fifty thousand cubic feet of salt due to a seemingly small, benign leak. As property values increase, such piles are being reshaped to take up less space, resulting in higher piles. Higher piles are more susceptible to large losses due to water infiltration.
Another problem with these, and many other tarpaulin systems having bands used for either banding or ballasting, is planning and installing the system so that the bands end up being properly oriented. In the case of a banded system, the bands must run generally vertically so that the ends of the bands may be anchored to create a downward force on the cover. A typical pile has a somewhat rectangular or racetrack shaped base. Positioning a tarp over the pile so the bands run vertically on the longer sides results in horizontal banding at the ends. To secure the ends, the tarp must be folded strategically to produce banding at the ends with at least some vertical component. Alternatively, the tarp may customized with multidirectional banding suited to each individual pile.
Customized tarps present yet another problem. After the protected commodity is distributed and consumed, the tarp owner is left with a great deal of material which was designed specifically for a pile which no longer exists. Though tarp material, in general, is useful and versatile, the irregular, custom-designed banding rarely lends itself to a variety of uses other than covering; the pile for which it was designed.
There is a need for a tarpaulin system that is strong, watertight, versatile and reusable.
The present invention relates to a tarpaulin system incorporating a plurality of reinforcing cords and durable, waterproof seams. As will become readily evident, the extreme versatility of the present invention is of such breadth that the number of uses for such a system is limited only by the imagination of the user.
The tarpaulin system of the present invention is comprised of a synthetic, waterproof material such as coated or laminated reinforced vinyl, polyvinyl, polyethylene, polypropylene, Hypalon(copyright), a chlorosulfonated polyethylene (CSPE)-based synthetic rubber developed by DuPont(copyright), or any such suitable waterproof synthetic material which is heat reactive and thus capable of being heat welded or bonded. Preferably, the material chosen comprises a woven polyester reinforcing scrim with either a coating or thermally bonded outer layer of one of the aforesaid plastic or rubber materials.
The aforementioned reinforcing cords may be natural rope but are preferably synthetic rope material such as polyethylene, polypropylene, polyester, and nylon or an aramid fiber like Kevlar(copyright), made by DuPont(copyright). The reinforcing cords are preferably folded into the material and tightly encapsulated and sealed therein by thermally welding the opposed fold sections together around the cords. This advantageously permits the transfer of stress loads from the cover fabric to the cords.
Heat welding is the preferred method of joining two pieces of the sheet material of the present invention together. Heat welding is the process of subjecting two pieces of the material to an elevated temperature sufficient to melt the outer layer of the material and subsequently pressing the two pieces together, thereby creating a bond as the pieces cool. Heat welding is advantageous because it bonds the two pieces together without puncturing, or otherwise breaching the watertight integrity of the material, unlike stitching or similar joining methods.
Heat welding results in a bond which is characterized by a high resistance to separation when subjected to stresses coplanar with the bond. Seams formed in the cover of the present invention that are oriented such that stresses will necessarily be relatively coplanar with the bond are herein referred to as xe2x80x9clap seamsxe2x80x9d or xe2x80x9clap weldsxe2x80x9d. FIG. 5 shows an example of a lap seam.
Heat welded bonds or seams on laminate or coating reinforced cover fabrics are only as strong as the adhesion of the laminate or coating to the scrim sheet, commonly referred to as the peel strength. When the two welded pieces are pulled away from each other using forces perpendicular to the plane of the bond in a peeling action, that peel strength is relatively low. Seams formed in the cover of the present invention that are oriented such that stresses will necessarily be relatively perpendicular to the bond are herein referred to as xe2x80x9cprayer seamsxe2x80x9d. FIG. 6 shows an example of a prayer seam.
Prayer seams are used in the present invention to envelop the reinforcing cord. Because the orientation of the cord is such that any forces the cord encounters will be in a direction away from or parallel to the seam, the prayer seam just needs to be strong enough to restrain the cord so that it does not become separated from the tarp.
However, the material will be subjected to forces easily capable of separating the prayer seam. To prevent this separation, the present invention preferably uses chokers or choker strips, when necessary, which transfer these forces to lap seams. The shear strength of a lap seam is directly proportionate to the width of the lap seam. This is because a lap seam, when subject to stress, distributes the stress over the entire area of the seam. Therefore, it is important to make a lap seam wide enough to support foreseeable stresses. Prayer seams, on the other hand, focus all of the stresses they are subject to, on the extreme edge of the seam in a peeling action. As the seam peels apart, the stresses are redirected to wherever the edge still intact is located. It follows that the strength of a prayer seam is independent of its width. As is hereinafter set forth in the description of the seaming method and structure, the seam stress is reoriented from a peeling action to a shear force on the choker strip lap joints.
By encapsulating the reinforcing cords into the body of the cover in a thermally welded fold seam of the cover, and strengthening that seam by a thermally welded choker strip, the strength of the cover is enhanced and stresses on it are relieved.
Preferably, the prayer seams used to envelop the cords are wide enough, and the chokers used to support them are of an appropriate width, to permit secondary uses for the cords and prayer seams. For instance, wide prayer seams result in significant parallel folds running the length of the tarp seams. If the tarp is placed on the pile such that these folds run horizontally, a fold could be attached to the adjacent fold above it by simply using plastic ties or ropes, thereby creating a trough for catching and directing rain water off of the pile. These troughs could also be used to carry pipes and pumping systems for directing rain water off of the pile and pumping it to a remote location.
It is envisioned that, due to its versatility, the present tarpaulin system herein described could be used to cover objects other than piles without significant modifications to the tarp itself. For instance, it is often desirable to cover waste ponds in order to control the odors and gases emitted therefrom and also to prevent excess rain water from mixing with the contents of the pond, thereby causing it to overflow and pollute the surrounding areas.
By erecting at least one, preferably two or more frames around the pond, the tarp could be placed over the pond at such a height as to provide a slope from a highest point at the top of one of the frames, to the ground around the perimeter of the pond. A fresh water channel surrounding the perimeter collects the fresh water and directs it to an acceptable location. The troughs of the tarp, described above, assist in directing the rain water from the tarp to the channel. A vent in the top of the tarp is used, preferably in connection with a duct, for venting the undesirable gasses away from the pond to an appropriate area.
It is also contemplated that the tarp may be placed flat over: a pond with freely extending ends of the aforesaid cords attached to anchoring devices, such as posts. With the cords thus tensioned, the seam folds in which they are tightly encapsulated will be caused to stand upright. Water collecting troughs are thus formed between adjacent cord fold sections.
These and other objectives and advantages of the invention will appear more fully from the following description, made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views. And, although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiments have been described, the details may be changed without departing from the invention, which is defined by the claims.